Perforating guns have been used for decades to perforate either a cased hole at a desired depth, or to perforate an open hole. In some applications, the perforating gun simply needs to be at the correct depth for the gun to be fired and the well desirably perforated. In other applications, however, the perforating charges located on the perforating gun must be oriented in a desired direction prior to detonation. It is a requirement that the gun be properly oriented prior to detonation in hydraulically fractured wells, and also to electrically sensored or “smart” wells. When hydraulically fracturing a well, injection pressure may be reduced and the flow rates increased if the perforating holes for receiving the charges are correctly aligned with the direction of principal maximum stress. For smart wells, it is important that the gun be properly oriented so that perforating does not injure or destroy the electronic sensors and/or communication lines in the well.
The use of perforating guns in a well has historically also involved the use of a bow spring decentralizer, decentralizing magnets, or offset weight devices. A weight selectively placed on one side of the gun should result in the gun being properly oriented by the weight device against the low side of the well. Decentralizers and decentralizing magnets employ their own system for trying to position a particular side of the gun against the low side of the well. All these devices become less effective when the well has a low angle from vertical. Many systems currently require the well operator to perform an orienting run prior to firing the perforating gun, so that the orientation of the gun with respect to the zone to be perforated may be determined for the run, then this information used to offset the gun to the desired orientation within the well. Orienting runs are commonly analyzed in conjunction with known well survey data in order to provide the required orientation of the gun in a well. These systems incur high costs due to the guidance packages, take valuable time for obtaining the relevant data then orienting the tool in response to that data, then firing the guns. In many applications, the orientation of the gun is “rechecked” by another run after the data has been initially obtained and the tool hopefully oriented to its proper position. The high shock loads caused by firing the gun particularly results in damage to the guidance system.
The disadvantages of the prior art are overcome by the present invention, and an improved perforating gun and method are hereinafter disclosed.